1. Field of the Invention
This invention relates to an optical disc drive for playing back or recording and playing back an optical disc and a method of controlling rotation number of a spindle motor for rotating the optical disc.
2. Description of the Prior Art
There are known optical disc drives for recording and playing back (reproducing) an optical disc such as a CD (compact disc), CD-ROM, CD-R (CD-Recordable) and CD-RW.
These optical disc drives are equipped with a motor (spindle motor) for rotationally driving the optical disc when recording and playing back (reproducing) the optical disc. The motor is driven under the rotation number control (rotation speed control). This control is called as a spindle servo.
Such rotation number control is mainly carried out based on the information read out from the optical disc by the optical pick-up. Namely, in the case of optical discs to which no data has yet been recorded, such control is carried out based on WOBBLE PWM signal outputted from the WOBBLE servo controller. This method of the spindle servo is called as a WOBBLE servo. On the other hand, in the case of optical discs to which data has been recorded, such control is carried out based on EFM PWM signal outputted from the CD servo controller. This method of the spindle servo is called as an EFM servo.
In these optical disc drives, there is a case that the rotation speed of the optical disc (that is, the rotation number of the optical disc in a predetermined period) is required to change during the rotation of the optical disc. For example, such a change is to be carried out when the optical disc rotating at a reference rotation speed (1xc3x97) is accelerated to the six times rotation speed (6xc3x97).
In this case, the WOBBLE servo or the EFM servo is once turned off, and then the spindle motor is kicked (that is, accelerated by applying a full level voltage to the spindle motor) in a predetermined time, and after the predetermined time, the WOBBLE servo or the EFM servo Is turned on again to perform the spindle servo so that the rotation speed reaches the target rotation speed. However, this method involves the following problem.
According to the spindle servo using the WOBBLE servo or the EFM servo, it is not possible to obtain (read out) the information from the optical disc until the increased rotation speed of the optical disc becomes a predetermined speed. Further, it is difficult to increase the gain of the servo since hunching is likely to occur by doing so. Therefore, it takes a relatively long time until the rotation number reaches the target rotation number and the rotation becomes stable (hereinafter, this time is referred to as xe2x80x9ctime until obtaining stabilityxe2x80x9d).
Further, in the optical disc drive, the rotation number of the optical disc differs between the case where the optical pick-up is in the inner region and the case where the optical pick-up is in the outer region (the former case is faster than the later case for 2.5 times at the maximum) in order to obtain the constant linear velocity. In the optical disc drive described above, when the optical pickup has been moved along the radial direction, the WOBBLE servo or EFM servo is also operated for controlling the rotation number of the motor. Therefore, when the optical pick-up is moved (jumped) from e.g. the outer region to the inner region, there arises the same problem as discussed above.
Further, during the increasing of the rotation speed of the motor to a different rotation speed level and during the movement (jump) of the optical pick-up, the spindle servo (WOBBLE servo or the EFM servo) does not work as described above.
In view of the above problem, the object of the present invention is to provide an optical disc drive which can obtain the stable rotation in a short time when the rotation number of the motor is to be changed.
Further, another object of the present invention is to provide a method of controlling rotation number of a spindle motor which drive which can obtain the stable rotation in a short time when the rotation number of the motor is to be.
In order to achieve the object, the present invention is directed to an optical disc drive which comprises: a motor for rotating an optical disc; an optical pick-up which can move at least in a radial direction of the optical disc; a sensor for detecting the rotation of the motor; and rotation number control means for controlling the rotation number of the motor based on signals from the sensor; wherein the rotation number control means is adapted to be used at the time of changing the rotation number of the motor.
As described above, according to the optical disc drive of the present invention, since the rotation number control at the time of changing the rotation speed of the motor is carried out by the rotation number control means using the signals from the sensor which detects rotation of the motor, it takes only a relatively short time until the changed rotation speed of the motor reaches the target rotation speed and its rotation becomes stable.
Preferably, the optical disc drive is constructed so that the rotation speed of the motor can be selectively changed in multiple steps given by integral multiples of 1, and the rotation number control means is used when the rotation speed of the motor is to be changed between the multiple steps.
Further, in the case where the optical disc drive is constructed so that the rotation speed of the motor is changed depending on the radial position of the optical pick-up with respect to the optical, the rotation number control means may be used when the rotation speed of the motor is to be changed due to movement of the optical pick-up in the radial direction of the optical disc.
Further, it is also preferred that the optical disc drive comprises another rotation number control means for controlling the rotation number of the motor based on information obtained from the optical disc, wherein the rotation number control at the time of changing the rotation number of the motor is carried out by the rotation number control means based on the signals from the sensor in place of the another rotation number control means based on the information obtained from the optical disc.
In the optical disc drives mentioned above, it is preferred that the sensor is constructed from a Hall element which generates a predetermined frequency, and the rotation number control means controls the rotation number of the motor based on the frequency from the Hall element so that the rotation number of the motor becomes a predetermined target rotation number.
Another aspect of the present invention is directed to an optical disc drive which comprises: a motor for rotating an optical disc; an optical pick-up which can move at least in a radial direction of the optical disc; a sensor for detecting the rotation of the motor; and first rotation number control means for controlling the rotation number of the motor based on Information obtained from the optical disc; and a second rotation number control means for controlling the rotation number of the motor based on signals from the sensor, wherein the rotation number control of the motor at least at the time of changing the rotation speed of the motor is carried out by the second rotation number control means.
In this optical disc drive, it is preferred that the rotation number control of the motor before and after the changing of the rotation speed of the motor is carried out by the first rotation number control means.
In the optical disc drive, it is preferred that the sensor is constructed from a Hall element which outputs FG signals having a predetermined frequency, and the second rotation number control means includes a FG servo using the FG signals.
Further, in the optical disc drive, it is preferred that the first rotation number control means is a WOBBLE servo using WOBBLE PWM signals from the optical disc or an EFM servo using EFM PWM signals.
The other aspect of the present invention is directed to a method of controlling rotation number of a spindle motor for rotating an optical disc in an optical disc drive. The method comprises the steps of: performing a spindle servo with a first spindle servo means which controls the rotation number of the spindle motor based on information obtained from the optical disc; switching the first spindle servo means to a second spindle servo means which controls the rotation number of the spindle motor based on signals from a sensor which detects the rotation of the spindle motor; and changing the rotation speed of the spindle motor under the spindle servo provided by the second spindle servo means in such a manner that the rotation number of the spindle motor reaches a predetermined rotation number.
Preferably, the method further comprises the step of switching the second spindle servo means to the first spindle servo means after the rotation number of the spindle motor has reached the predetermined rotation number.
In this method, it is preferred that the rotation speed of the spindle motor is adapted to be changed in multiple steps given by integral multiples of 1, and the rotation speed changing step is carried out when the rotation speed of the motor is to be changed between the multiple steps.
Further, it is also preferred that the rotation speed of the spindle motor is adapted to be changed depending on the radial position of the optical pick-up with respect to the optical disc, and the rotation speed changing step is carried out when the rotation speed of the motor is to be changed due to the radial movement of the optical disc.
According to the method, it is also possible to shorten the time required until the increased rotation of the spindle motor reaches a target rotation number and it becomes stable.
Other objects, structures and advantages of the present invention will be apparent when the following description of the preferred embodiment is considered taken in conjunction with the accompanying drawings.